The present invention generally relates to a battery and a portable equipment, and more particularly, to a battery having a safety valve such as to reduce an internal pressure thereof when the internal pressure rises high and to a portable equipment using the battery.
Along with the widely spread use of portable equipments such as a portable telephone, a note book PC or the like in recent years, studies have been progressed on a battery for use in the equipments. A structure of a battery used in a portable equipment is described in, for example, Japanese Patent Laying-Open No. 7-296790(1995).
FIG. 23 is a perspective view of a battery described in the publication. Referring to FIG. 23, the battery is constructed of an electrode group 204, a rectangular prismatic battery case 205 housing the electrode group 204, an opening seal plate 212 sealing up the electrode group housed in the rectangular prismatic case 205.
The electrode group 204 is formed by rolling up a composite of an anode plate 201 and a cathode plate 202 with a separator 203 interposing therebetween into a whirl-like bundle.
The rectangular prismatic battery case 205 has an opening face A. The electrode group 204 is inserted into the case 205 through the opening face A. The rectangular prismatic battery case 205 has a space in the interior thereof. The rectangular prismatic case 205 is fabricated from an iron plate of 0.3 mm in thickness. The rectangular prismatic battery case 205 is filled with an electrolyte.
The opening seal plate 212 is constructed of a lid plate 209, a glass hermetic seal 211 and an anode terminal 210. The glass hermitic seal 211 is present between the opening seal plate 212 and the anode terminal 210.
The anode terminal 210 and an anode plate 201 are electrically connected to each other by an anode lead 208. The anode lead 208 is connected to the anode terminal 210 by means of resistance welding. Furthermore, the lid plate 209 is fixed to the rectangular prismatic battery case 205 by means of laser welding.
A gas vent is provided to the rectangular prismatic battery case 205. A rupture film 206 is provided so as to close the gas vent. An etched portion 207 small in thickness formed by etching is provided to the rupture film 206.
Such a prior art battery has cases where a temperature rises high therein due to various causes: as examples, a case where the battery is exposed to a high temperature, a case where internal or external short-circuit arises and a case where an excessive current discharge occurs to a rapid temperature increase. Especially in a case of a secondary battery, when charge is effected under application of an excessively high voltage in excess of a prescribed value, the battery would be heated to a high temperature.
When a battery is in a high temperature condition, an electrolyte evaporates to generate gas. Furthermore, the electrolyte also decomposes to generate gas. Since this gas is confined within the rectangular prismatic battery case 205, an internal pressure of the battery increases. A further increase in the internal pressure breaks the battery and in some cases, a human body would be exposed to a danger.
Such circumstances being considered, a rupture film 206 has been provided to the rectangular prismatic battery case 205 to cope with the breakage caused by a built-up internal pressure. The rupture film 206 works this way: When an internal pressure of a battery exceeds a prescribed value, the etched portion 207 of the rupture film 206 is first blown off to avoid the breakage of a battery body itself. Gas or an electrolyte is leaked out through the blown-off portion to prevent increase in the internal pressure of the battery. The battery shown in FIG. 23 is designed such that when the internal pressure thereof reaches 8.8xc3x97105 Pa, the rupture film 206 is broken.
In a construction as shown in FIG. 23, however, a necessity arises that the rupture film 206 is provided as a separate member from the rectangular prismatic battery case 205, which has produced a problem to cause increase in manufacture cost.
Therefore, the present invention has been made in order to solve the problem as described above.
It is accordingly an object of the present invention to provide a battery having a safety valve capable of suppressing an increase in manufacture cost while adopting a simple and easy construction and a portable equipment using the battery.
A battery according to the present invention has an exterior member and a safety valve. The exterior member is of a tube-like shape. The safety valve is provided to the exterior member to reduce an internal pressure of the battery. The exterior member includes a relatively thick portion and a relatively thin portion, wherein the relatively thin portion constitutes the safety valve.
In a battery of such a construction, since the safety valve can be formed with a difference in thickness of the exterior member, the safety valve can be provided without using a separate member. As a result, a construction thereof is simple and easy, thereby enabling suppression of increase in manufacture cost.
Furthermore, preferably, the safety valve is formed at a side face of the battery. In this case, the side face of the battery is generally larger in area than is each of a top face thereof and a bottom face thereof. For this reason, a large area safety valve can be formed at the side face, which causes the safety valve to operate at a low pressure, with the result that a level of safety is further increased.
Moreover, preferably, the relatively thin portion is formed so as to surround part of the relatively thick portion. In this case, the thin portion and the thick portion surrounded by the thin portion constitute the safety valve. Since an area of the portions is increased, the safety valve operates at a low pressure, thereby, enabling a level of safety to further increase.
Besides, preferably, at least one of a length, a thickness and a shape of the relatively thin portion and a total area of the relatively thin portion and a region surrounded by the relatively thin portion is adjusted to set an internal pressure of a battery at which the safety valve operates. In this case, the internal pressure of the battery at which the safety valve operates can be properly set, whereby there can be provided a battery with a higher reliability and a higher level of safety.
Furthermore, preferably, the battery further includes an electrode disposed in the region surrounded by the relatively thin portion. In this case, the safety valve can be formed when the electrode is formed; therefore, the safety valve can be formed without adding a new process step.
A portable equipment according to the present invention includes: a battery; and a body of the portable equipment to which the battery is mounted. The battery includes: an exterior member of a tube-like shape and a safety valve provided to said exterior member to reduce an internal pressure of the battery. The exterior member is constituted of a relatively thick portion and a relatively thin portion. The safety valve is located so as to face the body of the portable equipment.
In a portable equipment constructed in such a way, the safety valve is located so as to face the body of the portable equipment. Hence, even when the safety valve operates to eject high pressure gas or liquid, a pressure of the gas or the liquid is imposed only on the body of the portable equipment; so, no chance arises that the pressure acts on a man holding the portable equipment. As a result, a level of safety is improved compared with a portable equipment such as in which a safety valve has its aperture directed to a human body.
Still furthermore, preferably, the portable equipment further includes a shield member interposing between the battery and the body thereof. In this case, even when the safety valve operates to eject high pressure gas or liquid, the gas or liquid is blocked by the shield member such that no pressure is imposed directly on the body of the portable equipment. As a result, a failure of a portable equipment can be prevented, which enables a reliability to further increase.